Monolithic ZrO2 Research Articles

Fracture resistance of 3-unit monolithic ZrO2 ceramics FPDs with different preparation designs of the distal abutment - an in-vitro study

Masticatory pressure increases in the distal areas of the dentition. This should be considered when restoring partially edentulous patients with a metal-free fixed partial denture (FPD). An alternative abutment preparation design can be used in order to increase the materials' volume in the most fracture-prone "connector area" of an FPD. The increased size of the connection might positively influence the constructions' mechanical durability, thereby increasing its success and survivability. The aim of the present study was to investigate the influence of two preparation designs of the distal abutment on the fracture resistance of three-unit, monolithic, ZrO2 FPDs. 3D printed replicas of a partially edentulous mandibular segment and a ZrO2, milled in full-contour, three-unit FPDs were used for this investigation. Two experimental groups (n=10 ) were defined based on the preparation design of the distal abutment tooth - classical shoulder preparation 0.8mm deep, and endocrown preparation with a 2-mm retention cavity. The bridge - mandibular segment replica assembly was done with relyXU200(3M ESPE, USA), light-cured for 10 seconds per side with D-light Duo (GC, Europe). After cementation the test specimens were subjected to loading in a universal testing machine Zwick (Zwick-Roell Group, Germany). Statistical analysis was performed using R and includes descriptive statistics, t-test for quantitative and chi-squared test for qualitative variables. The results showed no difference between the two studied groups in the maximum force required to fracture the test specimens [t=-1.8088 (17.39), p-value=0.087; P>0.05]. 95% of the fracture lines were located in the distal connector. Within the limitations of this study, it can be concluded that both tested preparation designs show similar results in terms of the load required to fracture the test specimens. Furthermore, it is confirmed that the distal connector is the weakest area of an all-ceramic 3-unit FPD in the posterior area.

Influence of the Addition of Ni‐Coated Carbon Nanotubes on the Mechanical Properties of Highly Porous Zirconia Cellular Structures

Herein, the effect of the addition of Ni‐coated carbon nanotubes (CNTs) on the microstructure, mechanical properties, and morphology of zirconia porous cellular structures is studied, aiming to increase their mechanical strength. Highly porous structures of monolithic zirconia (ZrO2) and zirconia reinforced with Ni‐doped CNTs (ZrO2 + CNT/Ni) are fabricated through the replica method. Scanning electron microscopy and micro‐computed tomography (microCT) analyses show that ZrO2 + CNT/Ni specimens present lower overall porosity (88.0%) than monolithic ZrO2 (93.8%), indicating improved sintering kinetics. Compressive tests for the ZrO2 + CNT/Ni samples result in a compressive strength of 0.82 ± 0.10 MPa, a threefold value of that of the monolithic sample (0.25 ± 0.07 MPa). The ZrO2 + CNT/Ni samples also present a higher elastic modulus (41.02 ± 4.94 MPa) than the ZrO2 ones (21.92 ± 5.40 MPa). Thus, the addition of Ni‐coated CNTs significantly improves the strength of highly porous zirconia cellular structures.

Time-efficiency and cost-analysis comparing three digital workflows for treatment with monolithic zirconia implant fixed dental prostheses: A double-blinded RCT

ObjectivesThis double-blinded randomized controlled trial investigated economic performance indicators (EPI) in terms of time-efficiency and production costs of 3-unit monolithic zirconium-dioxide (ZrO2) implant fixed dental prostheses (iFDP) in three different workflows. MethodsTwenty patients with two Straumann Tissue-Level-Implants received three iFDPs; two were fabricated in proprietary complete digital workflows with intraoral optical scanning and model-free fabrication with company-related CAD/CAM lab-software while one iFDP was manufactured on digitized casts from conventional impressions. The sequence of impression-taking for the three workflows (TRIOS 3/3Shape [Test-1]; Virtuo Vivo/Dental Wings [Test-2]; Impregum/3M Espe [Control]) was randomly allocated. Sixty iFDPs bonded to ti-base abutments were analyzed. Clinical and technical worksteps for Test-1/Test-2/Control were recorded and evaluated for time-efficiency including cost-analysis (CHF=Swiss Francs) using ANOVA-Tests (significance level α=0.05). ResultsMean total work time, as the sum of clinical plus technical steps, was 97.5 min (SD ± 23.6) for Test-1, 193.1 min (SD ± 25.2) for Test-2, and 172.6 min (SD ± 27.4) for Control. Times were significantly different between Test-1/Test-2 (p < 0.00001), Test-1/Control (p < 0.00001), and Test-2/Control (p < 0.03610). Technical costs were 566 CHF (SD ± 49.3) for Test-1, 711 CHF (SD ± 78.8) for Test-2, 812 CHF (SD ± 89.6) for Control, and were also significantly different for all comparisons (p < 0.00001). ConclusionsTest-1 demonstrated the best performance for time-efficiency, Test-2 revealed the worst result. This indicates that digital workflows are not the same and not necessarily superior to analog workflows of monolithic ZrO2 iFDPs. Complexity decreases by reducing the number of steps following complete digital workflows, resulting in lower production costs compared to the mixed analog-digital workflow with conventional impressions. Clinical significanceComplete digital workflows comprising intraoral optical scanning without physical models for treatment with monolithic ZrO2 iFDPs is an efficient alternative to mixed analog-digital workflows with conventional impressions and labside digitization of dental casts.

A Double-Blind Crossover RCT Analyzing Technical and Clinical Performance of Monolithic ZrO2 Implant Fixed Dental Prostheses (iFDP) in Three Different Digital Workflows.

This double-blind randomized controlled trial with a crossover design analyzed the technical and clinical performance of three-unit monolithic ZrO2 implant-fixed dental prostheses (iFDPs), prepared using two complete digital workflows (Test-1, Test-2) and one mixed analog–digital workflow (Control). Each of the 20 study patients received three iFDPs, resulting in 60 restorations for analysis. The quality of the restorations was assessed by analyzing laboratory cross-mounting and calculating the chairside adjustment time required during fitting. All iFDPs could be produced successfully with all three workflows. The highest cross-mounting success rate was observed for the original pairing iFDP/model of the Control group. Overall, 60% of iFDPs prepared with Test-1 workflow did not require chairside adjustment compared with 50% for Test-2 and 30% for Controls. The mean total chairside adjustment time, as the sum of interproximal, pontic, and occlusal corrections was 2.59 ± 2.51 min (Control), 2.88 ± 2.86 min (Test-1), and 3.87 ± 3.02 min (Test-2). All tested workflows were feasible for treatment with iFDPs in posterior sites on a soft tissue level type implant system. For clinical routine, it has to be considered that chairside adjustments may be necessary, at least in every second patient, independent on the workflow used.

Development of Ti dispersed ZrO2 composites and their room-temperature crack-healing behaviors

ZrO2-Ti composites containing 0–30 vol% Ti were fabricated by hot-press sintering method at 1350 °C from mixtures of ZrO2 (Here, 3 mol% yttrium-doped tetragonal-stabilized zirconia, 3Y-TZP) and TiH2 powders. The effects of Ti content on microstructures, mechanical properties, and electrical conductivity were investigated. Surface cracks induced in ZrO2-Ti composites were healed using electrochemical anodization technique at room temperature to recover the degraded flexural strength. ZrO2-15 vol% Ti exhibited the highest fracture toughness with the value of 6.76 MPa·m1/2, which increased by 21% compared to monolithic ZrO2. Composites containing more than 15 vol% Ti exhibited excellent electrical conductivity (∼100 Ωcm). The percolation threshold volume for electrical conduction in the present system was calculated to be 13.9 vol%. Based on the excellent electrical conductivity, electrochemical anodization process was used to heal cracks introduced on the surface of these composites. After anodization with a current density of 2 A/dm2 for 3 h at room temperature, composites containing a crack of 112 μm in length and 0.3 μm in width was completely healed with a fully recovered flexural strength.

Mechanochemical Synthesis and Rapid Consolidation of Nanostructured Nb–ZrO2 Composite

Nb₂O5 and Zr powders at a molar ratio of 1:2.5 were milled using a high-energy ball mill. The mixture powders produced Nb and ZrO₂ nanopowders through a solid replacement reaction (Nb₂O5+ 2.5Zr 2Nb + 2.5ZrO₂). The synthesized nanopowders were consolidated via high-frequency induction heated sintering (HFIHS) within two min. The mechanical properties (hardness and fracture toughness) of nanostructured 2Nb-2.5ZrO₂ composite were then evaluated. Both the hardness and fracture toughness of the 2Nb-2.5ZrO₂ composite were higher than those of monolithic ZrO₂.

In vitro shear bond strength of 2 resin cements to zirconia and lithium disilicate: An in vitro study

Statement of problemThere is little evidence on how the multiple layers of zirconia (ZrO2) or glazed material will affect the shear bond strength (SBS) of different resin cements. PurposeThe purpose of this in vitro study was to compare the SBS of 2 resin cements with the different layers of a monolithic polychromatic ZrO2 ceramic, both glazed and nonglazed, and a lithium disilicate (LDS) ceramic. Material and methodsOne hundred and sixty-eight composite resin cylinders and 48 monolithic polychromic ZrO2 plates were prepared. Twenty-four were milled and sintered, and 24 were milled and sintered and had a glaze cycle applied with no liquid glaze. These plates and 12 LDS plates were mounted in autopolymerized acrylic resin. Bonding surfaces were polished, airborne-particle abraded, and cleaned ultrasonically. The different layers (cubic, hybrid, and tetragonal) of the ZrO2 plates were identified and marked. The plates were assigned to 2 cement groups: a self-adhesive, autopolymerized resin cement, and a dual-polymerizing, adhesive resin cement (DPRC). Bonding surfaces were cleaned and treated according to the cement manufacturer’s instructions. Three composite resin cylinders were luted to the ZrO2 plates at the appropriate layer, and 2 cylinders were luted to each LDS plate. The specimens were stored in a moist environment for 24 hours at 37 °C. The SBS test was performed with a universal testing machine. Visual inspections of the debonded surfaces were compared under magnification. The data were analyzed with a 2-way ANOVA and a subsequent Student t test (α=.05). ResultsThe 2-way ANOVA found no difference among luting agent and LDS and ZrO2. The SBSs of the nonglazed tetragonal and cubic layer to the ZrO2 were higher than to the surface exposed to a glazing cycle (P=.001). The bonded surfaces were examined tactilely and under ×3.5 magnification, followed by light and scanning electron microscopy and recorded as either adhesive, cohesive, or mixed. Almost all failures in the glazed ZrO2 were mixed and cohesive. However, more adhesive failures were observed in the DPRC group of nonglazed ZrO2. ConclusionsNo differences were found between the 2 luting agents for the LDS. For the ZrO2 cubic and tetragonal layers, the DPRC had higher bond strengths to the nonglazed surfaces.

Effect of Alumina Nanofibers Content on the Microstructure and Properties of ATZ Composites Fabricated by Spark Plasma Sintering

In this work, 3mol.% yttria-stabilized zirconia was used as a matrix for the fabrication of alumina toughened zirconia (ATZ) composites. Alumina nanofibers were reinforcing additives with an amount of 1, 5 and 10wt.%. Fully dense ATZ composites were obtained by spark plasma sintering. Microstructure observations of the composites showed the mixed fracture mode, which favorably affects the fracture toughness. It is shown that the fracture toughness and Vickers microhardness of ATZ composites were significantly improved by the addition of Al2O3 nanofibers compared with monolithic ZrO2. The fracture toughness of composite with 1wt.% nanofibers addition is 4.40MPa·m1/2. The microhardness of composite with 5wt.% nanofibers is 16.75GPa. The toughening and strengthening mechanisms were analyzed.

Synthesis and Rapid Consolidation of W-1.5 ZrO2 Composite

ZrO2 is a candidate material for hip and knee joint replacements because of its excellent combination of biocompatibility, corrosion resistance and low density. However, the drawback of pure ZrO2 is a low fracture toughness at room temperature. One of the most obvious tactics to cope with this problem is to fabricate a nanostructured composite material. Nanomaterials can be produced with improved mechanical properties(hardness and fracture toughness). The high-frequency induction heated sintering method takes advantage of simultaneously applying induced current and mechanical pressure during sintering. As a result, nanostructured materials can be achieved within very short time. In this study, W and ZrO2 nanopowders are mechanochemically synthesized from WO3 and Zr powders according to the reaction(WO3 + 3/2 Zr→W+ 3/2 ZrO2). The milled powders are then sintered using high-frequency induction heating within two minutes under the uniaxial pressure of 80MPa. The average fracture toughness and hardness of the nanostructured W-3/2 ZrO2 composite sintered at 1300°C are 540 kg/mm2 and 5 MPa·m1/2, respectively. The fracture toughness of the composite is higher than that of monolithic ZrO2. The phase and microstructure of the composite is also investigated by XRD and FE-SEM.

Monolithic zirconia aerogel from polyacetylacetonatozirconium precursor and ammonia hydroxide gel initiator: formation mechanism, mechanical strength and thermal properties.

Zirconia (ZrO2) aerogels are potential candidates for use at temperatures higher than those attainable with silica aerogels. However, fabricating a robust ZrO2 aerogel with a high thermal stability is still a challenge. The extreme electronegativity of Zr makes the hydrolysis and polycondensation of zirconium precursors difficult to control, leading to poor structural integrity and unsatisfactory physical properties. In the present research, we prepared a ZrO2 aerogel by using a synthetic zirconium precursor, namely polyacetylacetonatozirconium (PAZ), and ammonia hydroxide as the gel initiator. The ammonia hydroxide catalyzes the cross-linking of PAZ via promotion of the dehydration between hydroxyls in PAZ and the acetylacetonate group in PAZ binds the zirconium ion firmly upon the addition of ammonia hydroxide to avoid a gel precipitate. A monolithic ZrO2 aerogel with a large diameter size of 4.4 cm and high optical transmittance was achieved after drying. The surface area and pore volume of the as-dried ZrO2 aerogel were as high as 630.72 m2 g−1 and 5.12 cm3 g−1, respectively. They decreased to 188.62 m2 g−1 and 0.93 cm3 g−1 after being heat-treated at 1000 °C for 2 h. The best mechanical performances of the ZrO2 aerogels showed a compressive strength of 0.21 ± 0.05 MPa and a modulus of 1.9 ± 0.3 MPa with a density of 0.161 ± 0.008 g cm−3. Both pore structures and mechanical performances varied according to the ammonia hydroxide gel initiator used. The thermal insulating properties of the ZrO2 aerogel performed better than a silica aerogel blanket with a thermal conductivity of 0.020 W (m−1 K−1).

Rapid consolidation of a nanostructured Mo-reinforced ZrO2 composite

MoO3 and Zr powders at a molar ratio of 1:1.5 were milled using a high-energy ball mill. The mixture powders produced Mo and ZrO2 powders through a solid replacement reaction (MoO3+1.5Zr→Mo+1.5 ZrO2). The synthesized powders were consolidated via pulsed current activated sintering (PCAS) within 2min. The mechanical properties (hardness and fracture toughness) and microstructure were then evaluated. Both the hardness and fracture toughness of the Mo-1.5 ZrO2 composite were higher than those of monolithic ZrO2.

Microwave synthesis of chain-like zircona nanofibers through carbon-induced self-assembly growth

Chain-like zircona (ZrO2) nanofibers were prepared by microwave sintering without any surfactants or solid templates. Microwave sintering was conducted in a multimode microwave cavity with TE666 resonant mode at 2.45 GHz. Carbon particles were used to activate unique thermal processes when mixed with ZrO2 precursor. The sintering condition was at 1300°C for 10 min. Samples were characterized by XRD, SEM, TEM techniques. It was found that both monolithic and tetragonal ZrO2 co-existed in samples prepared fromthe mixture of ZrO2 precursors and carbon by either microwave or conventional sintering. Only m-ZrO2 exists in samples prepared by ZrO2 precursors without carbon. ZrO2 appeared as chain-like nanofibers, which might be attributed to a so-called carbon-induced self-assembly growth mechanism.

Enhanced toughness of zirconia ceramics with graphene platelets consolidated by spark plasma sintering

AbstractGraphene platelets reinforced zirconia (GPLs/ZrO2) composites were prepared by spark plasma sintering in the present work. The effects of GPLs content on the densification route, microstructure feather, mechanical properties, and aging behaviors of such composites were investigated. In spite of the impeding effect of GPLs, high relative density of 98% was achieved for the composites owing to the uniform dispersion of GPLs. The addition of GPLs contributed to enhanced fracture toughness of the composites; when the added content was 1.0 wt.%, its fracture toughness reached up to 8.6 MPa·m1/2. Also, aging behavior of the GPLs/ZrO2 composites was investigated at 134°C for 24 hours. The monolithic ZrO2 ceramic and GPLs/ZrO2 composites presented residual ratio of 55% and 72% in fracture toughness, respectively. Thus, the incorporation of GPLs inhibited phase transformation from tetragonal phase to monoclinic phase of zirconia.

Mechanochemical synthesis and fast consolidation of a nanostructured CoTi-ZrO2 composite by high-frequency induction heating

CoTi and ZrO2 nanopowders were mechanochemically synthesized from CoTiO3 and Zr powders according to the reaction (2CoTiO3+3Zr→2CoTi+3ZrO2). The milled powders were then consolidated using high frequency induction heated sintering (HFIHS) within one minute under the applied pressure of 80MPa. The average hardness and fracture toughness of the nanostructured 2CoTi-3ZrO2 composite sintered from high energy ball milled powder were 1205kg/mm2 and 6.9MPam1/2, respectively. The mechanical properties of composite were compared with those of monolithic CoTi and ZrO2, respectively.

Mechanical properties and rapid low-temperature consolidation of nanocrystalline Cu-ZrO2 composites by pulsed current activated heating

Metal-ceramic compositr can be obtained with an optimum combination of low density, high oxidation resistance, and high hardness of the ceramic and toughness of the metal. Therefore, metal matrix composites are recognized as candidates for aerospace, automotive, biomaterials, and defense applications. Despite its many attractive properties, the low fracture toughness of ZrO2 limits its wide application. One of the most obvious tactics to improve the mechanical properties has been to fabricate a nanostructured material and composite material. Nano-powders of Cu and ZrO2 were synthesized from 2CuO and Zr powders by high-energy ball milling. Nanocrystalline 2Cu-ZrO2 composite was consolidated within 5 minutes from mechanically synthesized powders of ZrO2 and 2Cu at low temperature, by a pulsed current activated sintering method. The relative density of the composite was 98.5%. The fracture toughness of 2Cu-ZrO2 composite in this study is higher than that of monolithic ZrO2, without great decrease of hardness.

Mechanical and electrical properties of chemically modified MWCNTs/3Y-TZP composites

In the present work, homogeneous dispersion of MWCNTs in ZrO2 matrix was achieved by the chemical modification of MWCNTs and the formation of noncovalent attachment between carboxyl acid (–COOH) groups on MWCNTs and ZrO2 particles to obtain better compatibility of MWCNTs in ZrO2 matrix. 3Y-TZP/4wt% MWCNTs composite exhibited the best indentation toughness of 6.24MPam1/2 increasing 31% over monolithic ZrO2. Nanoindentation measurements showed that Young׳s modulus, hardness and contact-damage-resistance decreased with increasing the MWCNTs content. Moreover, the electrical conductivity slightly increased for MWCNTs weight fraction below 1wt% and displayed a dramatic increment with a maximum corresponding to MWCNTs weight fraction of 4wt%, which can be described by the percolation theory.

Synthesis of monolithic zirconia aerogel via a nitric acid assisted epoxide addition method

Monolithic zirconia aerogels were prepared using zirconium oxychloride (ZrOCl2) as the precursor in the presence of the epoxide (PO) in both ethanol and mixed ethanol–water solutions, respectively. The effects of nitric acid and water contents on the gel formation behavior and the properties of the resulting aerogel were investigated. The results show that at a molar ratio of HNO3/ZrOCl2 of 1.0 and H2O/ZrOCl2 of 10, the translucent monolithic ZrO2 aerogels were obtained and they exhibited a well-developed mesoporous structure and a high specific surface area of 454 m2 g−1. The as-prepared aerogels were composed of mainly amorphous phase and a spot of ZrO2 crystal. After calcination at 750 °C for 2 h, the ZrO2 transformed into tetragonal phase. These results suggested that this HNO3-assisted epoxide addition method was a simple and controllable way to get translucent monolithic zirconia aerogels.

Toughening mechanism and thermal shock resistance of ZrO2 (3Y)/Fe28at-%Al composites evaluated by indentation techniques

Toughening mechanism and thermal shock resistance of monoclinic ZrO2 (3Y) and ZrO2 (3Y)/Fe28at-%Al composites were investigated by indentation techniques. ZrO2 (3Y)/Fe28at-%Al composites exhibited more pronounced R curve behaviour than the monolithic ZrO2 (3Y). Quantitative analysis of toughening behaviour indicated that the enhanced toughness was attributed to the synergistic effect between crack bridging toughening and phase transformation toughening. Thermal shock resistance of as prepared composite was evaluated by indentation–quench method. Compared with monoclinic ZrO2 (3Y), ZrO2 (3Y)/Fe28at-%Al composites had higher critical thermal shock temperature difference ΔTU at which cracks grow unstably. The thermal shock resistance parameters R, R′ and R′′′′ were also calculated to evaluate the thermal shock resistance. It was found that the addition of Fe28at-%Al particles could lead to higher KIC, thermal conductivity and lower Yong’s modulus, thus resulting in higher ΔTU values of ZrO2 (3Y)/Fe28at-%Al composites than monoclinc ZrO2 (3Y).

Design and fabrication of porous ZrO2/(ZrO2 + Ni) sandwich ceramics with low thermal conductivity and high strength

3Y–ZrO2/(3Y–ZrO2+Ni) sandwich ceramics were fabricated through cold isostatic pressing and pressureless sintering. Porous 3Y–ZrO2 ceramics with large connecting open pores and permeability were used as interlayers for insulation, whereas outer metal–ceramic layers were used as bearing loads. Microstructures and properties of the porous ZrO2 and ZrO2/(ZrO2+Ni) sandwich ceramics were investigated in detail. The ZrO2/(ZrO2+Ni) sandwich ceramics exhibited better mechanical properties than the monolithic porous ZrO2 ceramics at the same low thermal conductivity (approximately 0.85W/mK). The mechanical properties of the sandwich ceramics were influenced by metal toughening and sintering-induced residual thermal stress.

Synthesis of crack-free monolithic ZrO2 aerogel modified by SiO2

Crack-free monolithic ZrO2 aerogel modified by SiO2 (ZSA) has been prepared for the first time by aging ZrO2 gel in tetraethoxysilane solution and drying in supercritical fluid. The microstructure of ZSA was characterized by scanning electron microscope, Fourier transform infrared spectroscopy and transmission electron microscopy, etc. The influence of SiO2 on the structure and properties of ZrO2 aerogel was studied. The results indicate that hetero-linkage of Zr–O–Si and Si–O–Si band is formed after modified by SiO2. The compressive strength of ZSA is 0.419 MPa, the bulk density is merely 0.19 g/cm3 and the thermal conductivity of ZSA is as low as 0.021 W/m K.